The addition of a hydrazine compound to a silver halide photographic emulsion or developing solution is known in U.S. Pat. No. 3,730,727 (a developing solution obtained by combining ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (the use of hydrazine as an auxiliary developing agent for obtaining a direct positive color image), U.S. Pat. No. 3,386,831 (containing .beta.-monophenyl hydrazide of an aliphatic carboxylic acid as a stabilizer for a silver halide light-sensitive material), U.S. Pat. No. 2,419,975, and The Theory of Photographic Process (edited by Mees, 3rd Edition, 1966, page 281).
It is disclosed in this literature, particularly U.S. Pat. No. 2,419,975, that the addition of a hydrazine compound provides a high contrast negative image.
It is described in the above U.S. Pat. No. (2,419,975) specification that when a light-sensitive material comprising a silver chlorobromide emulsion containing a hydrazine is developed with a developing solution having a pH as high as 12.8, an extremely high contrast having a gamma value (.gamma.) of more than 10 can be obtained. However, a strong alkali developing solution having a pH of near 13 is easily subject to oxidation by air and thus unstable for prolonged storage or use.
A superhigh contrast photographic property having a gamma value of more than 10 is extremely useful in the photographic reproduction of continuous tone images or line images produced by dot images useful for photomechanical process, whether the image is a negative or positive image. For such a purpose, a silver chlorobromide photographic emulsion having a silver chloride content of more than 50 mol %, and preferably 75 mol % has heretofore been used. Furthermore, the development has heretofore been conducted by using a hydroquinone developing solution having an extremely low effective concentration of sulfite ions (generally 0.1 mol/l or less). However, this process is disadvantageous in that the developing solution is extremely unstable and, thus, cannot withstand storage for a period of time exceeding 3 days because of its low concentration of sulfite ions.
Furthermore, this process cannot provide high sensitivity because it requires use of a silver chlorobromide emulsion having a relatively high content of silver chloride. Therefore, it had been keenly desired to obtain a superhigh contrast photographic property useful for reproduction of dot images or line images by using a high sensitivity emulsion and a stable developing solution.
The present inventors disclosed silver halide photographic emulsions which provide an extremely high contrast negative photographic property when developed with a stable developing solution in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614, and 4,323,643. However, the present inventors found that acylhydrazine compounds used in these emulsions have some disadvantages.
That is, these conventional hydrazines are known to generate nitrogen gas during development. This nitrogen gas gathers in the film to form bubbles, to thereby reduce the quality of photographic images. Furthermore, when the gas flows into the developing solution, it has adverse influences on other photographic light-sensitive materials.
Furthermore, these conventional hydrazines are required in a large amount for increasing sensitization and contrast. If the light-sensitive material requires a high sensitivity in particular, and these conventional hydrazines are used in combination with other sensitizing techniques (e.g., enhancing chemical sensitization, using grains of larger size, or adding a compound for accelerating sensitization as described in U.S. Pat. Nos. 4,272,606 and 4,241,164), sensitization and fogging are accelerated with time during storage.
Therefore, a compound has been desired which eliminates generation of such bubbles and outflow of the bubbles into the developing solution causes no problems on stability with the passage of time, and provides an extremely high contrast photographic property with addition of an extremely small amount thereof.
It is described in U.S. Pat. Nos. 4,385,108 and 4,269,929 that the use of a hydrazine having a substituent which is easily adsorbed on the silver halide grains can provide an extremely high contrast negative gradation photographic property. Among these hydrazine compounds containing such an adsorptive group, those described in the above mentioned known examples are subject to desensitization with the passage of time during storage. Therefore, it is required to select compounds which cause no such problem.
On the other hand, there are various direct positive photographic processes among which two are the most useful. One is a process in which a previously fogged silver halide grain is exposed to light in the presence of a desensitizer, and then developed. The other is a process in which a silver halide emulsion containing a sensitive speck thereinside is exposed to light, and then developed in the presence of a nucleating agent. The present invention relates to the latter process. A silver halide emulsion which has a sensitive speck mainly inside silver halide grains so that a latent image is formed mainly inside the grains is called an internal latent image type silver halide emulsion and is distinguished from a silver halide grain which forms a latent image mainly on the surface thereof.
Examples of the process in which an internal latent image type silver halide photographic emulsion is surface-developed in the presence of a nucleating agent to obtain a direct positive image and photographic emulsions or light-sensitive materials to be used in such a process are found in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552 and 3,317,322, British Pat. Nos. 1,011,062, 1,151,363, 1,269,640 and 2,011,391, Japanese Patent Publication Nos. 29405/68 and 38164/74, and Japanese Patent Application (OPI) Nos. 16623/78, 137133/78, 79, 40629/79, 74536/79, 74729/79, 52055/80 and 90940/80 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
In the process for obtaining a direct positive image, the nucleating agent may be added to the developing solution. However, a better reversal effect can be obtained by adding the nucleating agent to a photographic emulsion layer in the light-sensitive material or other proper layers so that it is adsorbed on the surface of the silver halide grain.
As suitable nucleating agents which may be used in the above process for obtaining a direct positive image there are known hydrazines as described in U.S. Pat. Nos. 2,563,785 and 2,588,982, hydrazide and hydrazine compounds as described in U.S. Pat. No. 3,227,552, heterocyclic quaternary salt compounds as described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122, British Pat. No. 1,283,835 and Japanese Patent Application (OPI) Nos. 3426/77 and 69613/77, thiourea combined type acylphenylhydrazine compounds as described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511 and 4,276,364, and British Pat. No. 2,012,443, compounds having a heterocyclic thioamide in an adsorptive group as described in U.S. Pat. No. 4,080,207, phenylacylhydrazine compounds containing a heterocyclic group having a mercapto group as an adsorption group as described in British Pat. No. 2,011,397B, sensitizing dyes containing in the molecular structure a substituent having a nucleating action as described in U.S. Pat. No. 3,718,470, and hydrazine compounds as described in Japanese Patent Application (OPI) Nos. 200230/84, 212828/84 and 212829/84, and Research Disclosure, No. 23510 (November, 1953).
However, it has been found that these compounds do not have sufficient activity for nucleating agents. Furthermore, it has been found that those having a high activity are poor in shelf life.